This invention relates to a field emission cathode (hereinafter also referred to as "FEC"), and more particularly to a field emission cathode useful as an electron source for various kinds of equipments such as a display device, a microwave vacuum tube, a light source, an amplification element, a high-speed switching element, a sensor and the like.
A so-called vertical type field emission cathode which is one example of a field emission cathode is generally constructed as shown in FIG. 5. More particularly, the vertical type field emission cathode includes an insulating substrate 100 made of glass or the like and a cathode electrode 101 arranged on the substrate 101. On the cathode electrode 101 is a resistive layer 102 made of a silicon film or the like, and an insulating layer 103 made of Si0.sub.2 or the like is then provided on the resistive layer 102. The insulating layer 103 is formed with cavities 104 and a gate 105 is arranged on the insulating layer 103. The resistive layer 102 is provided on each of portions thereof positionally corresponding to the cavities 104 with an emitter 106 of a cone-like shape, which is connected through the resistive layer 102 to the cathode electrode 101 on the substrate 100.
In the conventional field emission cathode constructed as described above, when the application of a bias voltage of a suitable level to the gate 105 in relation to the emitters 106 causes an electric field to be produced between a tip end of each of the emitters 106 and the gate 105, so that electrons may be emitted from the tip end of the emitter.
In general, a vertical type field emission cathode often causes a large amount of pulse current to flow through emitters due to a failure or deterioration in insulation instantaneously when a switch is closed for starting the FEC, resulting in the emitters being damaged. The conventional vertical type field emission cathode constructed as described above does not lead to short-circuiting because the resistive layer 102 for current restriction is provided between the emitters 106 and the cathode electrode 101, to thereby effectively prevent occurrence of voltage drop sufficient to cause the emission of electrons from the emitters adjacent thereto to be deteriorated.
Nevertheless, the conventional field emission cathode including the resistive layer for current restriction has the following problems.
First, the resistive layer causes voltage drop as high as 10%, so that it is required to increase a drive voltage correspondingly. In other words, the conventional field emission cathode fails to reduce a drive voltage, because voltage drop in the resistive layer causes a waste of the drive voltage.
Also, the emitters are varied in electron emission efficiency from one another. Although the resistive layer somewhat restrains such variation, such restraint is insufficient, resulting in the variation deteriorating uniformity of luminance.